Microcoil vaso-occlusive device with multi-axis secondary configuration

ABSTRACT

A vaso-occlusive device includes a microcoil formed into a minimum energy state secondary configuration comprising a plurality of curved segments, each defining a discrete axis, whereby the device, in its minimum energy state configuration, defines multiple axes. In a preferred embodiment, the minimum energy state secondary configuration comprises a plurality of tangentially-interconnected, substantially circular loops defining a plurality of discrete axes. In an alternative embodiment, the minimum energy state secondary configuration defines a wave-form like structure comprising a longitudinal array of laterally-alternating open loops defining a plurality of separate axes. In either embodiment, the device, in its minimum energy state secondary configuration, has a dimension that is substantially larger than the largest dimension of the vascular site in which the device is to be deployed. Thus, when the device is deployed in an aneurysm, the confinement of the device within the aneurysm causes the device to assume a three-dimensional configuration that has a higher energy state than the minimum energy state. Because the minimum energy state of the device is larger (in at least one dimension) than the aneurysm, the deployed device is constrained by its intimate contact with the walls of the aneurysm from returning to its minimum energy state configuration. Therefore, the device still engages the surrounding aneurysm wall surface, thereby minimizing shifting or tumbling due to blood flow dynamics. Furthermore, the minimum energy state secondary configuration (to which the device attempts to revert) is not one that is conducive to “coin stacking”, thereby minimizing the degree of compaction that is experienced.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable

FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

BACKGROUND OF THE INVENTION

[0003] This invention relates generally to the field of vascularocclusion devices and methods. More specifically, it relates to anapparatus and method for occluding a blood vessel by embolizing atargeted site (such as an aneurysm) in the blood vessel.

[0004] The embolization of blood vessels is desired in a number ofclinical situations. For example, vascular embolization has been used tocontrol vascular bleeding, to occlude the blood supply to tumors, and toocclude vascular aneurysms, particularly intracranial aneurysms. Inrecent years, vascular embolization for the treatment of aneurysms hasreceived much attention. Several different treatment modalities havebeen employed in the prior art. U.S. Pat. No. 4,819,637—Dormandy, Jr. etal., for example, describes a vascular embolization system that employsa detachable balloon delivered to the aneurysm site by an intravascularcatheter. The balloon is carried into the aneurysm at the tip of thecatheter, and it is inflated inside the aneurysm with a solidifyingfluid (typically a polymerizable resin or gel) to occlude the aneurysm.The balloon is then detached from the catheter by gentle traction on thecatheter. While the balloon-type embolization device can provide aneffective occlusion of many types of aneurysms, it is difficult toretrieve or move after the solidifying fluid sets, and it is difficultto visualize unless it is filled with a contrast material. Furthermore,there are risks of balloon rupture during inflation and of prematuredetachment of the balloon from the catheter.

[0005] Another approach is the direct injection of a liquid polymerembolic agent into the vascular site to be occluded. One type of liquidpolymer used in the direct injection technique is a rapidly polymerizingliquid, such as a cyanoacrylate resin, particularly isobutylcyanoacrylate, that is delivered to the target site as a liquid, andthen is polymerized in situ. Alternatively, a liquid polymer that isprecipitated at the target site from a carrier solution has been used.An example of this type of embolic agent is a cellulose acetate polymermixed with bismuth trioxide and dissolved in dimethyl sulfoxide (DMSO).Another type is ethylene glycol copolymer dissolved in DMSO. On contactwith blood, the DMSO diffuses out, and the polymer precipitates out andrapidly hardens into an embolic mass that conforms to the shape of theaneurysm. Other examples of materials used in this “direct injection”method are disclosed in the following U.S. Pat. Nos: 4,551,132—Pasztoret al.; U.S. Pat. No. 4,795,741—Leshchiner et al.; U.S. Pat. No.5,525,334—Ito et al.; and U.S. Pat. No. 5,580,568—Greffet al.

[0006] The direct injection of liquid polymer embolic agents has provendifficult in practice. For example, migration of the polymeric materialfrom the aneurysm and into the adjacent blood vessel has presented aproblem. In addition, visualization of the embolization materialrequires that a contrasting agent be mixed with it, and selectingembolization materials and contrasting agents that are mutuallycompatible may result in performance compromises that are less thanoptimal. Furthermore, precise control of the deployment of the polymericembolization material is difficult, leading to the risk of improperplacement and/or premature solidification of the material. Moreover,once the embolization material is deployed and solidified, it isdifficult to move or retrieve.

[0007] Another approach that has shown promise is the use ofthrombogenic microcoils. These microcoils may be made of a biocompatiblemetal alloy (typically platinum and tungsten) or a suitable polymer. Ifmade of metal, the coil may be provided with Dacron fibers to increasethrombogenicity. The coil is deployed through a microcatheter to thevascular site. Examples of microcoils are disclosed in the followingU.S. Pat. No.: 4,994,069—Ritchart et al.; U.S. Pat. No.5,122,136—Guglielmi et al.; U.S. Pat. No. 5,133,731—Butler et al.; U.S.Pat. No. 5,226,911—Chee et al.; U.S. Pat. No. 5,304,194—Chee et al.;U.S. Pat. No. 5,312,415—Palermo; U.S. Pat. No. 5,382,259—Phelps et al.;U.S. Pat. No. 5,382,260—Dormandy, Jr. et al.; U.S. Pat. No.5,476,472—Dormandy, Jr. et al.; U.S. Pat. No. 5,578,074—Mirigian; U.S.Pat. No. 5,582,619—Ken; U.S. Pat. No. 5,624,461—Mariant; U.S. Pat. No.5,639,277—Mariant et al.; U.S. Pat. No. 5,658,308—Snyder; U.S. Pat. No.5,690,667—Gia; U.S. Pat. No. 5,690,671—McGurk et al.; U.S. Pat. No.5,700,258—Mirigian et al.; U.S. Pat. No. 5,718,711—Berenstein et al.;U.S. Pat. No. 5,891,058—Taki et al.; U.S. Pat. No. 6,013,084—Ken et al.;U.S. Pat. No. 6,015,424—Rosenbluth et al.; and Des. U.S. Pat. No.427,680—Mariant et al.

[0008] While many prior art microcoil devices have met with some successin treating small aneurysms with relatively narrow necks, it has beenrecognized that the most commonly used microcoil vaso-occlusive devicesachieve less than satisfactory results in wide-necked aneurysms,particularly in the cerebrum. This has led to the development ofthree-dimensional microcoil devices, such as those disclosed in U.S.Pat. No. 5,645,558—Horton; U.S. Pat. No. 5,911,731—Pham et al.; and U.S.Pat. No. 5,957,948—Mariant (the latter two being in a class of devicesknown as “three-dimensional Guglielmi detachable coils”, or “3D-GDC's”).See, e.g., Tan et al., “The Feasibility of Three-Dimensional GuglielmiDetachable Coil for Embolisation of Wide Neck Cerebral Aneurysms,”Interventional Neuroradiology, Vol. 6, pp. 53-57 (June, 2000); Cloft etal., “Use of Three-Dimensional Guglielmi Detachable Coils in theTreatment of Wide-necked Cerebral Aneurysms,” American Journal ofNeuroradiology, Vol. 21, pp. 1312-1314 (August, 2000).

[0009] The typical three-dimensional microcoil is formed from a lengthof wire that is formed first into a primary configuration of a helicalcoil, and then into a secondary configuration that is one of a varietyof three-dimensional shapes. The minimum energy state of this type ofmicrocoil is its three-dimensional secondary configuration. Whendeployed inside an aneurysm, these devices assume a three-dimensionalconfiguration, typically a somewhat spherical configuration, that is ator slightly greater than, the minimum energy state of the secondaryconfiguration. Because the overall dimensions of these devices in theirnon-minimum energy state configuration is approximately equal to orsmaller than the interior dimensions of the aneurysm, there is nothingto constrain the device from shifting or tumbling within the aneurysmdue to blood flow dynamics.

[0010] In some of these three-dimensional devices (e.g., U.S. Pat. No.5,122,136—Guglielmi et al.), the secondary configuration is itself ahelix or some similar form that defines a longitudinal axis. Deviceswith what may be termed a “longitudinal” secondary configuration form athree-dimensional non-minimum energy state configuration when deployedinside an aneurysm, but, once deployed, they have displayed a tendencyto revert to their minimum energy state configurations. This, in turn,results in compaction due to “coin stacking” (i.e., returning to thesecondary helical configuration), thereby allowing recanalization of theaneurysm.

[0011] There has thus been a long-felt, but as yet unsatisfied need fora microcoil vaso-occlusive device that has the advantages of many of theprior art microcoil devices, but that can be used effectively to treataneurysms of many different sizes configurations, and in particularthose with large neck widths. It would be advantageous for such a deviceto be compatible for use with existing guidewire and microcathetermicrocoil delivery mechanisms, and to be capable of being manufacturedat costs comparable with those of prior art microcoil devices.

SUMMARY OF THE INVENTION

[0012] Broadly, the present invention is a microcoil vaso-occlusivedevice that has a minimum energy state secondary configurationcomprising a plurality of curved segments, each defining a discreteaxis, whereby the device, in its minimum energy state configuration,defines multiple axes. More specifically, each segment defines a planeand an axis that is substantially perpendicular to the plane.

[0013] In a particular preferred embodiment, the present invention is anelongate microcoil structure having a minimum energy state secondaryconfiguration that defines a plurality of tangentially-interconnected,substantially circular loops defining a plurality of separate axes. Inone form of the preferred embodiment, the substantially circular closedloops are substantially coplanar and define axes that are substantiallyparallel. That is, the planes defined by the segments are themselvessubstantially coplanar. In another form of the preferred embodiment,each pair of adjacent loops defines a shallow angle, whereby theirrespective axes define an angle of not more than about 90°, andpreferably not more than about 45°, between them.

[0014] In an alternative embodiment, the microcoil structure has aminimum energy state secondary configuration that defines a wave-formlike structure comprising a longitudinal array of laterally-alternatingopen loops defining a plurality of separate axes. As in the preferredembodiment, the alternative embodiment may be in a first form in whichthe loops are substantially coplanar and their respective axes aresubstantially parallel, or in a second form in which each pair ofadjacent loops defines a shallow angle, whereby their respective axesdefine an angle of not more than about 90°, and preferably not more thanabout 45°, between them.

[0015] In either embodiment, the device, in its minimum energy statesecondary configuration, has a dimension that is substantially larger(preferably at least about 25% greater) than the largest dimension ofthe vascular space in which the device is to be deployed. Thus, when thedevice is deployed inside a vascular site such as an aneurysm, theconfinement of the device within the site causes the device to assume athree-dimensional configuration that has a higher energy state than theminimum energy state. Because the minimum energy state of the device islarger (in at least one dimension) than the space in which it isdeployed, the deployed device is constrained by its intimate contactwith the walls of the aneurysm from returning to its minimum energystate configuration. Therefore, the device still engages the surroundinganeurysm wall surface, thereby minimizing shifting or tumbling due toblood flow dynamics. Furthermore, the minimum energy state secondaryconfiguration (to which the device attempts to revert) is not one thatis conducive to “coin stacking”, thereby minimizing the degree ofcompaction that is experienced.

[0016] As will be better appreciated from the detailed description thatfollows, the present invention provides for effective embolization ofvascular structures (particularly aneurysms) having a wide variety ofshapes and sizes. It is especially advantageous for use in wide-neckedaneurysms. Furthermore, as will be described in more detail below, thepresent invention may be deployed using conventional deploymentmechanisms, such as microcatheters and guidewires.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a perspective view of a microcoil vaso-occlusive devicein accordance with a preferred embodiment of the present invention;

[0018]FIG. 2 is a partial view of the device of FIG. 1, taken within thearea designated by the numeral 2 in FIG. 1;

[0019]FIGS. 3 and 4 are partial views of a microcoil vaso-occlusivedevice in accordance with another form of the preferred embodiment ofthe present invention;

[0020]FIG. 5 is a plan view of a microcoil vaso-occlusive device inaccordance with an alternative embodiment of the invention;

[0021]FIG. 6 is an elevational view of the present invention in theprocess of being deployed through a microcatheter into a wide-neckedaneurysm; and

[0022]FIG. 7 is a perspective view of a heat treatment fixture used tomanufacture the preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Referring first to FIGS. 1-4 and 8, a microcoil vaso-occlusivedevice 10, in accordance with a preferred embodiment of the invention isshown. The device 10 comprises a suitable length of wire formed into theprimary configuration of a helical microcoil 12 (FIG. 2). Suitablematerials for the device 10 include platinum, rhodium, palladium,rhenium, tungsten, gold, silver, tantalum, and various alloys of thesemetals. Various surgical grade stainless steels may also be used.Preferred materials include the platinum/tungsten alloy known asPlatinum 479 (92% Pt, 8% W, available from Sigmund Cohn, of MountVernon, N.Y.) and titanium/nickel alloys (such as the titanium/nickelalloy known as “nitinol”). Another material that may be advantageous isa bimetallic wire comprising a highly elastic metal with a highlyradiopaque metal. Such a bimetallic wire would also be resistant topermanent deformation. An example of such a bimetallic wire is a productcomprising a nitinol outer layer and an inner core of pure referencegrade platinum, available from Sigmund Cohn, of Mount Vernon, N.Y., andAnomet Products, of Shrewsbury, Mass. Wire diameters of about 0.0125 mmto about 0.150 mm may be used.

[0024] The microcoil 12 has a diameter that is typically in the range ofabout 0.125 mm to about 0.625 mm, with a preferred a preferred range,for most neurovascular applications, of about 0.25 mm to about 0.40 mm.The axial length of the microcoil 12 may be anywhere from about 5 mm toabout 1000 mm, with about 20 mm to about 400 mm being typical.

[0025] The primary winding of the microcoil 12 is applied under tension.The amount of tension, and the pitch of the primary winding, determinethe stiffness of the microcoil 12. These parameters can be varied alongthe length of the microcoil 12 to form a microcoil having differentdegrees of stiffness along its length, which may be advantageous incertain applications.

[0026] The microcoil 12 is formed into a secondary configuration thatcomprises a plurality of curved segments, each defining an axis, wherebythe microcoil 12 defines multiple axes. More specifically, each of thecurved segments defines a plane an axis that is substantiallyperpendicular to the plane. In the preferred embodiment of FIGS. 1-4,the curved segments are tangentially-interconnected, substantiallycircular loops 14 a, 14 b defining a plurality of separate axes 16. Inone form of the preferred embodiment, shown in FIG. 1, the substantiallycircular loops 14 a, 14 b are substantially coplanar and define axes 16that are substantially parallel. In another form of the preferredembodiment, shown in FIGS. 3 and 4, each pair of adjacent loops 14 a, 14b defines a shallow angle, whereby their respective axes 16 define anangle (θ₁, θ₂, θ₃, and θ₄) of not more than about 90° between them, andpreferably not more than about 45°.

[0027] The preferred embodiment of the invention typically includes apair of end loops 14 a and at least one intermediate loop 14 b.Typically, there will be up to four intermediate loops 14 b, dependingon the vascular site to be embolized, but there may be as many as six ormore, for use in very large vascular sites. The intermediate loops aresized to have a diameter approximately equal to the maximum diameter ofthe target vascular site (e.g., an aneurysm), while the end loops 14 ahave a slightly smaller diameter (preferably, approximately 1.5 mmsmaller), for purposes to be described below.

[0028] The primary microcoil 12 is formed into the secondaryconfiguration by heat treatment, as is well known in the art. Forexample, the annealed primary coil may be initially placed into thesecondary configuration by winding or wrapping around a suitably shapedand sized mandrel of refractory material, and then subjected to anannealing temperature for a specified period of time. For Platinum 479,for example, an annealing temperature of about 500° C. to about 1000°C., preferably approximately 670° C., is maintained for about 30 to 90minutes, preferably about 60 minutes, then cooled to room temperatureand ultrasonically cleaned. The resultant secondary configuration isthereby made permanent, and it becomes the minimum energy stateconfiguration of the microcoil 12.

[0029]FIG. 7 shows a heat treatment fixture 50 used in the manufactureof the preferred embodiment of the invention. The fixture 50 is made ofa refractory material, and it includes a base 52 having a surface onwhich is provided a mandrel for the secondary winding. The mandrelcomprises a plurality of winding pins 54 a, 54 b extending upwardly fromthe surface of the base 52. The exemplary fixture 50 shown in thedrawing has six pins arranged in roughly a hexagonal pattern. There aretwo end winding pins 54 a adjacent each other, and four intermediatewinding pins 54 b. A pair of fastening pegs 56 is located near one endof the fixture, for fastening the ends of the primary coil 12.

[0030] The diameters of the end winding pins 54 a are slightly smallerthan the diameters of the intermediate winding pins 54 b to achieve thesize relationships described above. The spacings between the pins 54 a,54 b are only slightly greater than the diameter of the primary coil 12,so that only one wind of the primary coil can be passed around the pinswith each winding of the secondary coil. Each subsequent winding of thesecondary coil is thus stacked on top of the previous winding. Thiseliminates any straight sections in the secondary coil, which, duringdeployment, would tend to push the coil into the parent artery.

[0031] During the secondary winding process, the primary coil 12 is keptunder tension. The amount of tension can be adjusted to control thedegree of spring-back of the loops 14 a, 14 b of the microcoil 12.

[0032] The secondary winding of the microcoil 12 is performed so thatthe loops 14 a, 14 b reverse direction as the microcoil 12 is wrappedaround each successive pin on the fixture. This ensures that loops willnot coin stack, and that they will disperse randomly throughout theaneurysm once deployed. Furthermore, in the preferred embodiment, eachloop is wound a complete 360° before the next loop is wound. Thisensures that each loop will completely seat within the aneurysm beforethe microcoil 12 reverses direction. With a complete loop intact, theloop strength is maximized, and the loop distributes loads evenly.

[0033]FIG. 5 shows a microcoil vaso-occlusion device 20 in accordancewith an alternative embodiment of the invention. This embodimentincludes a primary microcoil 22 formed into a secondary minimum energystate configuration that defines a wave-form like structure comprising alongitudinal array of laterally-alternating open loops 24 defining aplurality of separate axes 26. As in the preferred embodiment, thealternative embodiment may be in a first form in which the loops 24 aresubstantially coplanar and their respective axes 26 are substantiallyparallel, or in a second form in which each pair of adjacent loops 24defines a shallow angle, whereby their respective axes 26 define anangle of not more than about 90°, and preferably not more than about45°, between them. The materials, dimensions, and method of manufactureof this alternative embodiment are, in all material respects, similar tothose of the preferred embodiment described above.

[0034] The method of using the present invention is shown in FIG. 6. Inuse, the proximal end of the microcoil 12 (or 22) is attached to thedistal end of a guidewire or microcatheter (not shown). The attachmentmay be by any of a number of ways known in the art, as exemplified bythe following U.S. patents, the disclosures of which are expresslyincorporated herein by reference: U.S. Pat. No. 5,108,407—Geremia etal.; U.S. Pat. No. 5,122,136—Guglielmi et al.; U.S. Pat. No.5,234,437—Sepetka; U.S. Pat. No. 5,261,916—Engelson; U.S. Pat. No.5,304,195—Twyford, Jr. et al.; U.S. Pat. No. 5,312,415—Palermo; U.S.Pat. No. 5,423,829—Pham et al.; U.S. Pat. No. 5,522,836—Palermo; U.S.Pat. No. 5,645,564—Northrup et al.; U.S. Pat. No. 5,725,546—Samson; U.S.Pat. No. 5,800,453—Gia; U.S. Pat. No. 5,814,062—Sepetka et al.; U.S.Pat. No. 5,911,737—Lee et al.; U.S. Pat. No. 5,989,242—Saadat et al.;U.S. Pat. No. 6,022,369—Jacobsen et al. U.S. Pat. No. 6,063,100—Diaz etal.; U.S. Pat. No. 6,068,644—Lulo et al.; and U.S. Pat. No.6,102,933—Lee et al.

[0035] A target vascular site is visualized, by conventional means,well-known in the art. The target vascular site may be an aneurysm 40branching off a parent artery 42. The aneurysm 40 has a dome 44connected to the branch artery by a neck 46. A catheter 30 is passedintravascularly until it enters the dome 44 of the aneurysm 40 via theneck 46. The microcoil 12 is passed through the catheter 30 with theassistance of the guidewire or microcatheter until the microcoil 12enters the dome 44 of the aneurysm 40.

[0036] The undersized end loop 14 a at the distal end of the microcoil12 enters the aneurysm first. This assists in seating the first loopproperly, because the smaller size keeps the first loop inside the neck46 of the aneurysm, avoiding the parent artery 42.

[0037] The intermediate loops 14 b then enter the aneurysm. Because theyare sized to fit the aneurysm, they can deploy freely and smoothly withminimal friction against the wall of the aneurysm. Because the secondaryconfiguration of the microcoil 12 is essentially coplanar, all of theintermediate loops exert a force against the walls of the aneurysm dome44, thereby improving the resistance of the microcoil 12 to shifting dueto pulsatile blood flow.

[0038] As the microcoil 12 enters the aneurysm, it attempts to assumeits secondary configuration. Because the microcoil, in its secondaryconfiguration, is larger than the aneurysm, however, it is constrainedinto a deployed configuration in which it tends to fill the interiorvolume of the aneurysm. In this deployed configuration, the microcoil isin an energy state that is substantially higher than its minimum energystate. Thus, when the device is deployed inside a vascular site such asan aneurysm, the confinement of the device within the site causes thedevice to assume a three-dimensional configuration that has a higherenergy state than the minimum energy state. Because the minimum energystate of the device is larger (in at least one dimension) than the spacein which it is deployed, the deployed device is constrained by itsintimate contact with the walls of the aneurysm from returning to itsminimum energy state configuration. Therefore, the device still engagesthe surrounding aneurysm wall surface, thereby minimizing shifting ortumbling due to blood flow dynamics. Furthermore, the minimum energystate secondary configuration (to which the device attempts to revert)is not one that is conducive to “coin stacking”, thereby minimizing thedegree of compaction that is experienced.

[0039] The undersized end loop 14 a at the proximal end of the microcoil12 enters the aneurysm last. After the microcoil is fully deployed, itis controllably detached from the guidewire by any suitable meanswell-known in the art, thereby allowing the microcatheter or guidewireto be withdrawn, leaving the microcoil in place to embolize theaneurysm. After detachment, the proximal end loop 14 a curls into theneck 46 of the aneurysm 40, avoiding the parent artery 42.

[0040] The present invention thus exhibits several advantages over priorart three-dimensional microcoils. For example, there is increasedcoverage of the aneurysm neck, due to the presence of loops across theneck, yet the probability of any part of the device intruding into theparent artery is reduced. The secondary coil configuration also providessmoother deployment, and, once deployed, the device exhibits greaterresistance to coil compaction, thereby increasing positional stabilityin the face of pulsatile blood flow. This stability is achieved withlower overall friction between the device and the aneurysm wall.Moreover, the random distribution of loops throughout the aneurysmallows the device to maintain a complex shape inside the aneurysm,yielding improved embolization.

[0041] While a preferred embodiment and an alternative embodiment of theinvention have been described herein, it will be appreciated that anumber of variations and modifications will suggest themselves to thoseskilled in the pertinent arts. For example, other secondaryconfigurations than those described herein may be found that will yieldmost, if not all, of the significant advantages of the invention fortreatment of the typical aneurysm, or that will prove especiallyadvantageous in specific clinical applications. Also, for specificapplications, the dimensions and materials may be varied from thosedisclosed herein if found to be advantageous. These and other variationsand modifications are considered to be within the spirit and scope ofthe invention, as defined in the claims that follow.

What is claimed is:
 1. A microcoil vaso-occlusive device comprising amicrocoil formed into a minimum energy state secondary configurationcomprising a plurality of curved segments, each defining a discreteaxis, whereby the device, in its minimum energy state configuration,defines multiple axes.
 2. The device of claim 1, wherein each of thecurved segments defines a plane and an axis that is substantiallyperpendicular to the plane.
 3. The device of claim 1, wherein themultiple axes are substantially parallel.
 4. The device of claim 1,wherein each adjacent pair of the multiple axes forms an acute angle. 5.The device of claim 1, wherein the curved segments are substantiallyclosed loops, interconnected to each other substantially tangentially.6. The device of claim 1, wherein the curved segments are wave-like openloops.
 7. The device of claim 1, wherein the microcoil is formed from abimetallic wire.
 8. The device of claim 7, wherein the bimetallic wireincludes a radiopaque metal and a super-elastic metal.
 9. The device ofclaim 8, wherein the bimetallic wire comprises a platinum core and anitinol outer layer.
 10. A microcoil vaso-occlusive device comprising amicrocoil formed into a minimum energy state secondary configurationcomprising a plurality of tangentially-interconnected substantiallycircular loops, each defining a plane and a discrete axis that issubstantially perpendicular to the plane.
 11. The device of claim 10,wherein the axes are substantially parallel.
 12. The device of claim 10,wherein each adjacent pair of the axes forms an acute angle.
 13. Thedevice of claim 10, wherein the microcoil is formed from a bimetallicwire.
 14. The device of claim 13, wherein the bimetallic wire includes aradiopaque metal and a super-elastic metal.
 15. The device of claim 14,wherein the bimetallic wire comprises a platinum core and a nitinolouter layer.
 16. A method of embolizing an aneurysm, comprising thesteps of: (a) providing microcoil vaso-occlusive device comprising amicrocoil formed into a minimum energy state secondary configurationcomprising a plurality of curved segments, each defining a discreteaxis, whereby the device, in its minimum energy state configuration,defines multiple axes and has at least one dimension that is larger thanthe interior dimension of the aneurysm; and (b) deploying the deviceinto the interior of the aneurysm so that device is contained within theaneurysm in a configuration having an energy state that is substantiallyhigher than its minimum energy state, whereby the device is constrainedby its contact with the aneurysm from returning to its minimum energystate configuration.
 17. The method of claim 16, wherein the device, init minimum energy state secondary configuration, comprises a pluralityof tangentially-interconnected, substantially circular loops, eachdefining a discrete axis.
 18. The method of claim 16, wherein thedevice, in its minimum energy state configuration, comprises a pluralityof interconnected wave-like open loops, each defining a discrete axis.